Instead, it says the company inspects concrete structures using infrared cameras, an inspection technology which measures the difference in temperature between "sound conditions and damaged areas" to detect potential weak points. There as no explicit reference to testing carried out on tunnels.
The Sasago Tunnel runs for 4.7 kilometers along a stretch of the Chuo Expressway which runs for 367 kilometers, through a mountainous region, connecting Tokyo with the Nagoya in the Chubu region of Japan.
Its operator, NEXCO-Central is one of three companies started in 1995 after the privatization of Japan's Highway Public Corporation. NEXCO-Central manages more than 1,700 kilometers of expressways in Tokyo and the Chubu, Hokuriku and Kinki regions, used by almost 1.9 million cars on any given day.